This invention relates to the preparation of triarylphosphines. This invention further relates to a novel catalyst for preparing triarylphosphines by the reaction between sodium, an aryl halide and a phosphorous trihalide.
The preparation of triphenylphosphine from sodium, phosphorous trichloride and chlorobenzene was reported in the patent literature as early as 1930 (German Pat. No. 508,667). This patent teaches that certain catalysts can be added for the purpose of reducing the length of the induction period, which can be as long as one hour. Following the induction period the reaction may begin violently and is often accompanied by a large increase in the temperature of the reaction mixture. The heat generated may be sufficient to decompose a portion of the reactants, thereby decreasing product yield and purity.
U.S. Pat. No. 3,723,536 teaches that aryl halides or a small amount of a previously prepared triarylphosphine can be employed as a catalyst for the preparation of triarylphosphines, however, it has been found that these catalysts may have the same disadvantages as catalysts disclosed in the aforementioned German patent.
It is therefore an objective of this invention to provide a catalyst for the reaction of sodium, a monohalogenated aromatic hydrocarbon and a phosphorus trihalide which will significantly reduce the induction period and the exothermic nature of this reaction while simultaneously improving product yield and purity. It has now been found that this objective can be achieved using a triarylphosphine dihalide as the catalyst for the reaction.